A starter-generator drive for use in aircraft is now well known in the art. An aircraft engine drives a constant frequency electrical generator. The aircraft engine can operate at variable speeds; therefore, it is necessary to have a constant speed drive driven by the engine which will provide constant speed power to the electrical generator, even though the engine may be operating at varying speeds. It is also known to use the same mechanism for starting the engine wherein the electrical generator is caused to operate as an electric motor for starting of the engine. The Aleem U.S. Pat. No. 3,786,696 is typical of such a starter-generator drive for use between an aircraft engine and a generator to transmit power in either direction. The Aleem patent has a differential and a hydrostatic transmission interconnected between the aircraft engine and the generator and the hydrostatic transmission is adjustable to provide a constant speed drive of the generator with varying speeds of the aircraft engine.
A more recent embodiment of a starter-generator drive is disclosed in the applicant's U.S. Pat. No. 4,315,442 which utilizes a differential and a hydrostatic transmission. The hydrostatic transmission is controlled to provide an energy-dissipating starting mode when the generator is operating as an electric motor to start the aircraft engine.
It is also known to utilize an electro-mechanical system for achieving a constant speed drive. The O'Mahony U.S. Pat. No. 3,468,193 discloses a constant speed drive utilizing a plurality of differentials and an electro-magnetic eddy current brake having an inductor which can be regulated to control the slip of the brake. The system includes a change speed device in the drive between an input shaft and an alternator to limit the amount of slip that occurs in the eddy current brake to avoid high power losses.
It is not known in the prior art to have a starter-generator drive utilizing a hydro-viscous dissipative clutch to provide both starter and generator drive functions and with an associated multi-speed transmission for changing the drive ratio between the engine and the dissipative clutch. The drive is smaller in size and weight and has improved reliability and cost advantages over the existing art and does not affect transmission of torque to the generator and, therefore, its speed when the multi-speed transmission changes ratios.